[Tutor] Exit from program early

Hi
In the example below I would like the program to stop if I forgot to
provide an argument . Though I could do all my processing indented under
the else statement, I was wondering if there was a command that would allow
me to halt the program execution early.
Regards,
Roy
# Example program - Test for valid argument
import sys
if len(sys.argv) < 2:
print "opps missing an argument"
# Nice if I could stop and exit program here
else:
print "Argument provided!!"
# Looking good so go do some stuff
print "Done some stuff"